This invention relates to a projection yoke for a color projection TV of the type having electron guns corresponding to three primary colors.
In general, a projection TV of this type includes three electron guns (beam projection tubes) disposed at different places and an optical system is utilized to project a large image on a screen. For this reason, it is essential to completely eliminate any drift of rasters from the individual tubes such that the three color images are perfectly matched on the screen. In order to accomplish this purpose, a projection yoke for such a use includes not only a main deflection yoke but also an auxiliary yoke (or a convergence yoke) for correcting dynamic convergence as shown, for example, in Japanese Utility Model Publication Jikkai 63-95160.
With reference now to FIG. 7 which shows a prior art projection yoke, numeral 21 indicates a main deflection yoke with a coil separator 22 to which a main vertical deflection coil 21a and a main horizontal deflection coil 21b are attached through a core 21c. An auxiliary deflection yoke 23 is attached to an enlarged back part 22a of this coil separator 22 by screws. Numeral 24 indicates a ring core to which auxiliary vertical and horizontal deflection coils are attached and, as shown in FIG. 8, has four protrusions 24a in its interior. The auxiliary vertical and horizontal deflection coils on bobbins 25 are adapted to be set thereonto. Because of these bobbins 25, however, the auxiliary deflection yoke 23 tends to be big, causing an increase in the cost as a whole.
With the structure as shown in FIG. 8, furthermore, the resultant magnetic field tends to be excessively barrel-shaped, adversely affecting the quality of the electron beams.